This invention is directed to means for providing a reciprocating piston type pump having an integral positively actuated valving mechanism enabling reversibility of flow and prevention of back flow without the use of check valves, slide valves, or rotating seals formerly required in the prior art. In the invention, the pistons function by their construction and actuation duty cycle to perform fluid intake, fluid discharge, and valve port closure in that order in three equal time phases, in contrast to prior art devices using the pistons in two equal time phases of fluid intake and fluid discharge and requiring separate inlet and discharge valves to prevent back flow. The invention thus permits dispensing with the check valves used in prior art hydraulic systems. The invention utilizes the pistons to accomplish all necessary valving in a manner not previously known by employing a resilient pad of compressible material on the piston top which is compressed between the piston and cylinder head after fluid is discharged from the cylinder. The invention provides a more reliable long wearing and positive valve closure than prior art valving devices because solid particles which may be present in the fluid and caught between the cylinder head and the piston pad are temporarily imbedded in the compressible material of the pad and do not prevent effective port closure. The invention thus permits dispensing with filters required on prior art hydraulic systems which have been subject to malfunction caused by solid particles in the fluid, and makes possible a simplified and more reliable hydraulic system. The invention employs an external annular piston drive wheel having cam slots on its sides to provide the piston actuation duty cycle by positive actuation of the cam follower equipped pistons in three cylinders radially disposed at three equal angles on a central stationary ducting and support member. In the invention each piston goes through its duty cycle in one revolution of the cam wheel, with the pistons successively phased in their duty cycles by the equal angular and symmetrical rise and fall portions on each side of the equal angular constant dwell portion of the cam. The invention thus permits a reversal of flow through the pump by a reversal of direction of cam wheel rotation while maintaining the same piston duty cycle but in reverse order of piston actuation. The invention permits dispensing with separate check valves formerly required with prior art devices when at rest because one piston is always positively locked in its port closed position by the dwell portion of the cam whether the cam is rotating or at rest thus always preventing any back flow through the pump. In the invention, fluid enters and leaves each cylinder via large cylinder head ports, impelled by the piston motion. The invention uses short direct constant diameter ducts and ports in a central stationary ducting member having no seals, thus providing higher efficiency and reliability than prior art devices requiring flow restricting separate valves or rotary seals. As the piston pad of the present invention has no sliding or rotating motion against its seat on the cylinder head and has a large area of contact, wear is minimized in comparison to prior art valving devices. The only moving seals used in the invention are the O-Rings on the reciprocating pistons. Due to the short cam driven piston stroke of the invention, the life of the O-Rings is comparatively long. In the invention, the employment of an external annular cam wheel and sealed ball bearings make possible the quick and easy disassembly of the pump for repair purposes and simple bearing renewal in contrast to prior art devices.